yan. 1 6, 1890] 



NATURE 



^S7 



Remarks. 

 (i) This is described in Herschel's general catalogue as "a 

 remarkable object, very large, round, with tail, much brighter 

 in the middle." The spectrum has not yet been recorded, but it 

 promises to be one of great interest, as the nebula is apparently 

 one of the cometic ones. The meteoritic hypothesis suggests 

 that tliese are produced by a condensed swarm moving at a high 

 velocity through a sheet of meteorites at rest, or a swarm almost 

 at rest surrounded by a moving sheet. In the former case the 

 collision region would be behind the swarm, and would be spread 

 out like a comet's tail, the angle of the fan and length of '* tail " 

 depending upon the velocity of the moving swarm. Observa- 

 tions for variations of spectrum between nucleus and tail will 

 also be valuable. 



(2) This is a typical example of stars of Group II. Observa- 

 tions similar to those suggested for 20 Leporis, U. A., last week, 

 are required. 



(3) Konkoly classes this with stars of the solar type. The usual 

 differential observations, as to whether the star belongs to Group 



III. or to Group V., are required. 



(4) In Gothard's list of star spectra this is described as Group 



IV. The usual observations are suggested. 



(5) Duner describes the spectrum of this star as Group VI., 

 but his description is not complete. The characters of the 

 different bands, especially of Band 6, require further observa- 

 tion. It may be remarked in connection with these stars of 

 small magnitude, that the observations are by no means so diffi- 

 cult as in the case of small stars with spectra consisting of fine 

 lines. The bands are broad and generally dark, so that the 

 continuous spectrum is broken up into zones. 



(6) This variable has a period of 167 days, and ranges in 

 magnitude from about 8 at maximum to 13 at minimum. The 

 spectrum is of the Group II. type, and, as in other variables of 

 the same group, bright lines mayaj^pear at maximum. Duner 

 states that the bands are very wide and dark, but he does not 

 state what bands are present. Maximum on January 18. 



(7) The spectrum of this variable has not yet been recorded, 

 but the colour indicates that it is probably either Group II. or 

 Group VI. The period is 228 days, and the range from 7 at 

 maximum to 10 at minimum. The maximum will occur on 

 Januarv 18. A. Fowler. 



The Temperature of the Moon. — Prof. Langley, by 

 means of the bolometer, made some measurements of the heat 

 from different parts of the eclipsed moon on the night of Sep- 

 tember 23, 1885 {Phil. Mag., January, 1890). These measure- 

 ments were made in connection with a much more extended 

 study on the temperature of our satellite. The following par- 

 ticulars are given : — The diameter of the lunar image was 

 28-3 millimetres, and of this only a limited portion (o 08 of the 

 whole) fell upon the bolometer. As the penumbra came on, 

 the diminution of heat was marked, being measured by the 

 bolometer even before the eye had detected any appearance of 

 shadow. The heat continued to diminish rapidly with the pro- 

 gress of the immersion in the penumbra. At one hour before 

 the middle of the total eclipse, the deflection in the umbra was 

 3*8 divisions. Fifty minutes after the middle of the eclipse, it 

 had diminished to approximately i "3 divisions, this being less 

 than I per cent, of the heat from a similar portion of the un- 

 eclipsed moon. The rise of the temperature after the passage 

 of the umbra was apparently nearly as rapid as the previous fall. 

 The most important conclusion drawn by Prof. Langley from 

 his researches is that the mean temperature of the sunlit lunar 

 soil is most probably not greatly above zero Centigrade. 



On the Orbit of Struve 228.— The Monthly Notices of 

 the Royal Astronomical Society, December 1889, contains a 

 note, communicated by Mr. J. E. Gore, on this binary star. 

 Recent measures show that, since Struve discovered the star in 

 1829, it has described about 120° of its apparent orbit. The 

 following provisional elements have been computed : — 



Elements of 2 228. 



P = 8873 years. 

 T = 1906 '03 



e = 0-5311 



i = 70° 59' 



a = 84 49 

 A = 51 36 



a = o"-98 

 M = +4° -057 



According to this orbit, the distance between the components 

 will gradually increase during the next few years up to a maxi- 

 mum of about o"-55, and then diminish again as the companion 

 approaches the periastron. The minimum distance will not be 



reached until the position angle is 180° (after the periastron pas- 

 sage), when the components will probably be separated by less 

 than o"-2. The binary lies a little preceding 62 Andromedae, 

 the position for 1890-0 being approximately — 



R.A. 2h. 6m. 59s., Decl. + 46° 58'-4. 

 The magnitudes of the components are about 6*7 and 7-6. 



Orbit of Swift's Comet (V. 1880). — The orbit of this 

 comet has been computed, by Gibbs's vector method, by Messrs, 

 W. Beebe and A. W. Phillips (Astr. yourn., Nos. 207, 208). 

 This method is found to possess advantages over those of Gauss 

 and Oppolzer. Below are given elements which have been 

 computed from eight observations ranging from October 25, 

 1880, to January 7, 1881, and compared with these are the 

 elements computed from three observations by Gibbs's method. 

 Both are referred to the ecliptic and mean equinox of 1880-0 : — 

 Eight observations. 'I hree observations. 



O / /' 



i = 5 22 2-03 



v- 0,= 106 13 I9'I7 

 9, = 296 52 2*09 

 log e = 9*8146985 

 log a = 0-4873065 



T= 1880 Nov. 7-782810 

 Periodic time = 1965-88 days. 

 On the Variability of R Vulpecul^. — Schcinfeld, from 

 a discussion of the observations from 1859 to 1874, found that 

 a uniform period left systematic deviations outstanding which 

 exceeded seven or eight times the uncertainty of the single 

 maxima, but that a quadratic term, corresponding to a shorten- 

 ing of o'i2 days from epoch to epoch, brought them within the 

 range of the probable errors. The divergence from observation, 

 however, soon began, and rapidly widened, until in 1885 it 

 amounted to 106-5 days. Mr. Chandler {Astr. yourn., No. 

 208) gives a table showing the maxima and minima observed 

 since 1807, with the deviations from the elements of his cata- 

 logue. It is seen that, whereas the difference between the ob- 

 served and the calculated maxima and minima, using Schonfeld's 

 elements, are very considerable, the elements given by the author 

 differed from those observed only in a very slight degree. 



On the Rotation of Mercury. — Nearly a century has 

 elapsed since Schroter published his first observation of the 

 physical aspect of Mercury, and assigned to the planet a period 

 of rotation ; but it has been left to that perspicacious observer, 

 Signor Schiaparelli, to demonstrate the fact by a series of re- 

 markable observations given by him in Astranomische Nach- 

 richten. No. 2944. The observations extend from 1882 to the 

 end of last year. As many as 150 drawings have been made of 

 the markings upon the planet with respect to the best positions 

 for observation. It is noted that one of the finest drawings was 

 made on August 11, 1882, when Mercury was only 3° 2' from 

 the sun's limb. The markings that are visible on Mercury when 

 observed at the same hour on consecutive days are identical in 

 their aspect, and this being so, three hypotheses have been pro- 

 pounded {Astr. Nach., 2479) regarding the rotation of the planet,, 

 viz. : — 



That (i) the lime of rotation is about 24 hours. 



(2) The planet makes two or more rotations in the same in- 

 terval. 



(3) The time of rotation is so slow as to be inappreciable when 

 observing the markings during a few days. 



Schroter decided in favour of the first hypothesis, and Bessel, 

 from a discussion of this observer's data, determined the time of 

 rotation to be 24h. om. 52 •97s. Schiaparelli's observations 

 support the last of these hypotheses, and are opposed to the 

 rotation period determined by Schroter. 



Following a series of dark markings, shown in the figure 

 which accompanies the article, it was found that — 



Mercury revolves round the sun in the same manner that the 

 moon revolves round the earth, always presenting to it the same 

 hemisphere ; hence, since the planet's periodic time is 87-9693 

 days, this must be the time of rotation on its axis. 



The dark markings observed appear extremely faint, and are 

 not easily recognized. On good occasions the colour may be 

 seen to be reddish-brown, and always differs from the general' 

 colour of the planet's disk, which is a bright rose changing to 

 copper. 



This most interesting and important communication from 

 Milan Observatory must be read in detail in order that it may 

 be appreciated. 



